gmirror, gjournal and glabel - which order?

[Vincent Hoffman]

krad wrote:
> 2009/10/13 Daniel Bye <freebsd-questions at slightlystrange.org>
>
>   
>> On Tue, Oct 13, 2009 at 01:08:46AM +0300, Manolis Kiagias wrote:
>>     
>>> Daniel Bye wrote:
>>>       
>>>> Hi all,
>>>>
>>>> I'm having a hard time trying to work out which order I should set up
>>>> gmirror, glabel and gjournal on a new system. I want to journal my
>>>> /home partition, label all the partitions for ease of reference, and
>>>> use gmirror to save me in the event a disk goes bad. I am struggling
>>>> to fit the pieces together conceptually in my mind. I understand the
>>>> processes involved in setting each part separately - my problem is in
>>>> trying to build this up in the right order so that it all makes sense.
>>>>
>>>> So far, I have labelled the primary drive and set up the journal. I
>>>>         
>> have
>>     
>>>> edited fstab to reflect the labels and journalled file system on /home.
>>>> If I now build a mirror, don't I need to alter fstab to mount that and
>>>> not the stuff in /dev/label? In which case, I guess I need to build the
>>>> mirror first, and then set up labels and journals?
>>>>
>>>> I'm going round and round in circles here and none of the stuff I've
>>>> read on the web enlightens me... :-/
>>>>
>>>> Any insights or suggestions would be taken as a great kindness!
>>>>
>>>> Dan
>>>>
>>>>
>>>>         
>>> When not mirroring,  I first create the journals and then label the
>>> resulting adxxxx.journal devices
>>> In case you are doing a gmirror device, you would not really need the
>>> separate label step - the gm device name won't change and gmirror is not
>>> affected if the device names of the individual disks change (the disks
>>> are marked as part of a mirror and scanned at startup).
>>> When you are creating the composite gmirror device you are effectively
>>> labeling it anyway i.e. gmirror label gm0...
>>> Now if you follow the usual tutorials found in the web you would be
>>> using gm0 / gm1 but you actually name it any way you wish.
>>> If you really need to label the separate gmirrored partitions, do it
>>> after setting up the mirror.
>>>
>>> Concerning the order of journals and mirroring, I  create the journals
>>> first, then mirror the result. This has always worked fine for me.
>>>       
>> Thanks much, Manoli. After posting, I came to more or less the same
>> conclusion, but it's good to get confirmation from someone who clearly
>> knows more about this stuff than I do!
>>
>> I'd still be interested to hear what others think/do.
>>
>> As ever, thanks for your time.
>>
>> Dan
>>
>> --
>> Daniel Bye
>>                                                                     _
>>                                              ASCII ribbon campaign ( )
>>                                         - against HTML, vCards and  X
>>                                - proprietary attachments in e-mail / \
>>
>>     
>
>
> I've always gmirrored 1st, then created the gjournal then newfs the journal
> device with the -L and -J flags to label it. I'm not sure if this is correct
> but ufs2 has hooks into gjournal, and if the journal class inst directly
> below the ufs layer these hooks might not work correctly.
>   

I've always done it this way too (mirror then journal,) both for the
reason given and because of the following from the gjournal(8) manpage:

     When gjournal is configured on top of gmirror(8) or graid3(8)
providers,
     it also keeps them in a consistent state, thus automatic
synchronization
     on power failure or system crash may be disabled on those providers.


Vince
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